LIARS!
I don't buy it =)
Voting to forfeit is quitting... you are just hoping teammates agree to avoid the ban. Quitting after a teammate quits first is still quitting. And then there is just regular old quitting. I rarely do that (maybe 2-3 times?) as I try to play out each game and in the situations where I do want to quit it's almost always 1v3 with no shot of a comeback (too many goals or too little time).
If you have never been in a situation where the game is totally out of reach, you are 1v3 facing assholes flaming chat w/one guy dedicated just to bumping / demoing you and maybe you had a shitty day on top of that or just some place else to be and didn't say screw it and throw in the towel... well... again I don't buy it.
I also don't buy it's good practice. Instead of playing the last 2 minutes 1v3 (abnormal game conditions) in an unwinnable game you could be playing the first 2 minutes of the next game 3v3 (normal game conditions). If you want to practice being shorthanded play unfair vs bots or you know in pretty much every game when your teammates don't rotate =) A huge part of the challenge of this game is playing with teammates. IMO any practice time spent in shorthanded situations is better spent playing with a full squad. But to each his own and if you are someone who honestly has never quit and feels doing so makes you a better player by all means go for it.